COVID-19 ICU Admissions, Deaths Associated With Old Age and Multimorbidity


The presence of 4 or more comorbidities was strongly associated with a higher risk of critical outcomes, regardless of vaccination status.

The majority of COVID-19 hospitalizations that resulted in intensive care unit admission or death occurred in patients who were older or had multiple comorbidities, according to recent research published in the journal Clinical Infectious Disease.1

Since the start of the COVID-19 pandemic in 2020, 6 million hospitalizations and over 1 million deaths have occurred in the US because of the disease. Factors that were associated with critical outcomes earlier in the pandemic have been known, but a lack of data exists for more recent periods with other variants of the virus.

“The number of patients hospitalized due to COVID-19 infection has decreased over time for a variety of reasons, including vaccination and natural immunity acquired due to past infection, advances in medical care as well as the severity of variants,” Brian Dixon, a co-author on the study, said in a release.2 “But the virus hasn’t gone away and it’s important to note that people are still being infected or reinfected and are being hospitalized.”

A team of investigators from the Regenstrief Institute in Indianapolis, Indiana conducted a study to explore the clinical profile of adults hospitalized with COVID-19 over time and identify risk factors associated with critical outcomes by vaccination status. The study was done within the CDC’s VISION Vaccine Effectiveness Network, a multi-state research collaboration that collects electronic health records of vaccinations from different health care systems.

Data was collected from 8 health care systems in 10 states from June 1, 2021 through March 29, 2023. The study cohort included 60488 hospitalized patients with a median age of 67 years, of which 51.6% were male and 69.3% were White. The patients were hospitalized with COVID-19 during the Delta period (June-December 2021) through the post-BA.4/BA.5 period (September 2022-March 2023).

Investigators found that the median age increased during the study period, from 60 to 75 years. Vaccinations increased from 18.2% to 70.1% and critical outcomes decreased from 24.8% to 19.4%. However, those with critical outcomes had a higher proportion of 4 or more comorbidities.

Additionally, the presence of 4 or more comorbidities was strongly associated with a higher risk of critical outcomes, regardless of vaccination status.

Study limitations include that clinical management may have changed throughout the study period, that prior infection was not reliably known, and an inability to determine if someone was hospitalized due to COVID-19 illness or other contributing conditions.

“This is one of the first studies to examine and describe how the characteristics of seriously ill COVID-19 patients and the risk factors associated with those hospitalizations changed over time,” Shaun Grannis, a co-author on the study, said in a release. “Our findings provide insight into factors that influence outcomes for hospitalized patients and can help us be alerted to those potential risks, so we can pay special attention to the most at-risk individuals.”

1. Griggs EP, Mitchell PK, Lazariu V, et al. Clinical epidemiology and risk factors for critical outcomes among vaccinated and unvaccinated adults hospitalized with COVID-19—VISION Network, 10 States, June 2021–March 2023, Clin Infect Dis. 2023;
2. COVID-infected adults with 4 or more underlying diseases or advanced age face higher risk of ICU stay, death. News Release. Regenstrief Institute. September 19, 2023. Accessed September 19, 2023.
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